Reference Sound Research Articles

Modified Multiple Stimulus With Hidden Reference and Anchors-Gabrielsson Total Impression Sound Quality Rating Comparisons for Speech in Quiet, Noise, and Reverberation.

The purpose of the study was to obtain, analyze, and compare subjective sound quality data for the same test stimuli using modified multistimulus MUSHRA (Multiple Stimulus with Hidden Reference and Anchors) based procedures (viz., MUSHRA with custom anchors and MUSHRA without anchor) and the single-stimulus Gabrielsson's total impression rating procedure. Twenty normally hearing young adults were recruited in this study. Participants completed sound quality ratings on two different hearing aid recording data sets-Data Set A contained speech recordings from four different hearing aids under a variety of noisy and processing conditions, and Data Set B contained speech recordings from a single hearing aid under a combination of different noisy, reverberant, and signal processing conditions. Recordings in both data sets were rated for their quality using the total impression rating procedure. In addition, quality ratings of Data Set A recordings were obtained using a MUSHRA with custom anchors, while the ratings of Data Set B recordings were collected using a MUSHRA without anchor. Statistical analyses revealed a high test-retest reliability of quality ratings for the same stimuli that were rated multiple times. In addition, high-interrater reliability was observed with all three rating procedures. Further analyses indicated (a) a high correlation between the total impression rating and the two modified MUSHRA ratings and (b) a similar relationship between the average and standard deviation of the subjective rating data obtained by the total impression rating and MUSHRA with custom anchors on Data Set A, and the total impression rating and the MUSHRA without anchor on Data Set B. Both sound quality procedures, namely, the MUSHRA-based procedures and the total impression rating scale, obtained similar quality ratings of varied hearing aid speech recordings with high reliability.

Round-robin testing on Sound power level measurement for Reference Sound Source and Office printer

Round-robin testing for two samples, Reference Sound Source in accordance with ISO 6926 and Office printer with electrophotographic engine, were executed by seven testing laboratories in Japan on 2020. All tests were executed with parallelepiped measurement surface in hemi anechoic chamber in accordance with testing standard for engineering-grade sound power determination, ISO 3744:2010. The results show that sample standard deviation for RSS is better than printer. Standard deviations for overall A-weighted sound power level for two samples are better than combined standard uncertainties calculated with reference example of standard deviations in ISO 3744 (1.5 dB for Reference Sound Source as standard deviation of operating/mounting condition is negligibly small, 1.6 dB for printer as stable operating/mounting condition 0.5 dB). This paper also indicates tips for those who would conduct round-robin testing to obtain valid results by obviating incorrect operations and malfunctions of printers or similar equipment from the experience of some round-robin tests.

Study on the Properties of Aerodynamic Reference Sound Sources

Towards the establishment of traceability in sound power in airborne sound, the present study focuses on the dissemination procedure. Aerodynamic reference sound sources were studied as potential transfer standards. Initially, the sources were examined in the up-to-present requirements. The core of the study is the correction required for the transition from calibration to in situ conditions. The influence of atmospheric pressure, ambient temperature and fan rotation speed was investigated and the corresponding correction was determined. A comparison to an existing correction was also performed. Near field effects were another part of the study. The related uncertainty was estimated in a transparent approach. The dependency of the uncertainty on the in situ and calibration condition values is also presented.

Sound power estimation with an acoustic camera in comparison with sound power determination using sound pressure and sound intensity method

Sound Power Level (SWL) is a measure to be used to describe a sound source regardless its surrounding and environment. In general, there are two different standardized methods to determine the Sound Power Level of a sound source, which are by using sound pressure and sound intensity. Other than that, there is a possibility to estimate Sound Power Level using an acoustic beamforming array or more popularly known as acoustic camera. This estimation is considered more time-efficient compared to the two methods and can be done when there are other sound sources during the measurement. However, this measurement is not yet standard compliant and therefore cannot be used for standardized reporting or legislative purposes.The paper highlights the possibility to estimate Sound Power Level of a Reference Sound Source using an acoustic beamforming array, when another sound source is present at the time of measurement. Besides comparing to the Reference Sound Source’s calibration chart, the measurement is compared with two ISO-compliant measurements which are ISO 3746 (Survey grade, sound pressure method) and ISO 9614-2 (survey grade, sound intensity method).

Leveraging diversity in computer-aided musical orchestration with an artificial immune system for multi-modal optimization

The aim of computer-aided musical orchestration (CAMO) is to find a combination of musical instrument sounds that perceptually approximates a reference sound when played together. The complexity of timbre perception and the combinatorial explosion of all possible musical instrument sound combinations make it very challenging to find even one orchestration for a reference sound. However, finding only one orchestration is seldom enough given the creative nature of the compositional process. Compositional applications of computer-aided musical orchestration can greatly benefit from multiple orchestrations with diversity. In this work, we use an artificial immune system (AIS) called opt-aiNet to search for combinations of musical instrument sounds that minimize the distance to a reference sound encoded in a fitness function. Opt-aiNet was developed to maximize diversity in the solution set of multi-modal optimization problems, which results in multiple alternative orchestrations for the same reference sound that are different among themselves. We compared the diversity and the similarity of the orchestrations proposed by opt-aiNet (CAMO-AIS) against a standard genetic algorithm (CAMO-GA) and Orchids, which is considered the state of the art for CAMO, for 13 reference sounds. In general, CAMO-AIS outperformed CAMO-GA and Orchids for several measures of objective diversity. We performed a listening test to evaluate and compare the perceptual similarity of the orchestrations by CAMO-AIS and Orchids. CAMO-AIS generated orchestrations that were perceived to be as similar to the reference sounds as those returned by Orchids. Therefore, CAMO-AIS has higher diversity of orchestrations than Orchids without loss of perceptual similarity.

Availability of Reference Sound Sources for Qualification of Hemi-Anechoic Rooms Based on Deviation of Sound Pressure Level from Inverse Square Law

The sound power level is a physical quantity indispensable for evaluating the amount of sound energy radiated from electrical and mechanical apparatuses. The precise determination of the sound power level requires the qualification of the measurement environment, such as a hemi-anechoic room, by estimating the deviation of the sound pressure level from the inverse-square law. In this respect, Annex A of ISO 3745 specifies the procedure for room qualification and defines a tolerance limit for the directivity of the sound source, which is used for the qualification. However, it is impractical to prepare a special loudspeaker only for room qualification. Thus, we developed a simulation method to investigate the influence of the sound source directivity on the measured deviation of the sound pressure level from the inverse-square law by introducing a quantitative index for the influence of the directivity. In this study, type 4202 reference sound source by Brüel & Kjær was used as a directional sound source because it has been widely used as a reference standard for the measurement of sound power levels. We experimentally obtained the directivity of the sound source by measuring the sound pressure level over the measurement surface. Moreover, the proposed method was applied to the qualification of several hemi-anechoic rooms, and we discussed the availability of a directional sound source for the process. Analytical results showed that available reference sound sources may be used for the evaluation of hemi-anechoic rooms depending on the sound energy absorption coefficient of the inner wall, the directionality of the microphone traverse, and the size of the space to be qualified. In other words, the results revealed that a reference sound source that is once quantified by the proposed method can be used for qualifying hemi-anechoic rooms.

Annoyance of low-level tonal sounds – Factors affecting the penalty

PurposeEnvironmental and appliance sounds involving tonal components can be more annoying than broad-band noise. Mandatory penalty values exist in many countries for tonal sound. The purpose of our study was to determine how tonal sounds are perceived compared to non-tonal sounds at overall levels close to typical regulated levels inside residential dwellings. MethodsForty participants rated the loudness and annoyance of tonal sounds and non-tonal reference sounds in laboratory conditions. The tonal frequencies were 50, 110, 290, 850 and 2100 Hz. Four levels of tonal audibility were used: 5, 10, 17 and 25 dB. The experiment was repeated using two overall levels of tonal sounds: 25 and 35 dB LAeq. Penalty was determined by finding an equally annoying reference sound. ResultsThe penalty depended on the tonal frequency and the tonal audibility. Penalty values were also different with different overall levels especially at high tonal frequencies. Annoyance penalty was zero at two lowest tonal frequencies 50 and 110 Hz. At other tonal frequencies, the penalty increased with increasing tonal audibility and tonal frequency. The largest value of penalty was 12 dB. It was obtained at tonal frequency 2100 Hz and with the largest level of tonal audibility. ConclusionsOur results are against the use of fixed penalty values, which are usual in many national regulations, when the overall level is low, within 25 and 35 dB LAeq. The results support the application of a step-wise penalty where the penalty depends on tonal frequency, tonal audibility and overall level.

Hearing Tests on Mobile Devices: Evaluation of the Reference Sound Level by Means of Biological Calibration.

BackgroundHearing tests carried out in home setting by means of mobile devices require previous calibration of the reference sound level. Mobile devices with bundled headphones create a possibility of applying the predefined level for a particular model as an alternative to calibrating each device separately.ObjectiveThe objective of this study was to determine the reference sound level for sets composed of a mobile device and bundled headphones.MethodsReference sound levels for Android-based mobile devices were determined using an open access mobile phone app by means of biological calibration, that is, in relation to the normal-hearing threshold. The examinations were conducted in 2 groups: an uncontrolled and a controlled one. In the uncontrolled group, the fully automated self-measurements were carried out in home conditions by 18- to 35-year-old subjects, without prior hearing problems, recruited online. Calibration was conducted as a preliminary step in preparation for further examination. In the controlled group, audiologist-assisted examinations were performed in a sound booth, on normal-hearing subjects verified through pure-tone audiometry, recruited offline from among the workers and patients of the clinic. In both the groups, the reference sound levels were determined on a subject’s mobile device using the Bekesy audiometry. The reference sound levels were compared between the groups. Intramodel and intermodel analyses were carried out as well.ResultsIn the uncontrolled group, 8988 calibrations were conducted on 8620 different devices representing 2040 models. In the controlled group, 158 calibrations (test and retest) were conducted on 79 devices representing 50 models. Result analysis was performed for 10 most frequently used models in both the groups. The difference in reference sound levels between uncontrolled and controlled groups was 1.50 dB (SD 4.42). The mean SD of the reference sound level determined for devices within the same model was 4.03 dB (95% CI 3.93-4.11). Statistically significant differences were found across models.ConclusionsReference sound levels determined in the uncontrolled group are comparable to the values obtained in the controlled group. This validates the use of biological calibration in the uncontrolled group for determining the predefined reference sound level for new devices. Moreover, due to a relatively small deviation of the reference sound level for devices of the same model, it is feasible to conduct hearing screening on devices calibrated with the predefined reference sound level.

Sound power measurement standards at laboratory and field environments

Sound power level measurements, SWLs, of equipment and machinery through direct or comparison methods at laboratory or field conditions, are of increasing importance in terms of regulations and industrial competitiveness. SWLs constitute the input data when modeling the real world, in complex industrial premises for example, as a means for diagnosis and SPL predictions. SWLs have a major technical and economical impact, trying to keep the measurement uncertainties as low as possible, while balancing the testing complexity, time consumption, and costs. In the present work, a description about the calibration of a Reference Sound Source, RSS, B&K 4204 [ISO 6926] is made. The testing survey of normal equipment emitting steady noise and the RSS at different acoustical environments, that range from an hemi-anechoic room to a typical industrial facility is also described. Some measuring methods such as ISO 3745, ISO 3744, ISO 9614-2 are compared for the different sources and environments, yielding some discrepancies between standards as is extensively referred to in literature. A proposal based on a new multiple height microphone array is encouraged at laboratory conditions. Regarding field tests, sound intensity measurements by scanning is extensively adopted for practical reasons, with acceptable results according to our experience.

Determination of reference sound source sound power levels using ARI Standard 250

The Air Conditioning and Refrigeration Institute (ARI) Standard 250 Performance and Calibration of Reference Sound Sources was used to establish one-third octave band sound power levels of several reference sound sources (RSS). The work was carried out in an anechoic chamber that was qualified at frequencies of 100 Hz and above using ANSI S12.35. Measurements were made with circular slices around the RSS at heights from 5 cm to 195 cm in 10 cm increments using both intensity and sound pressure. A 19 point fixed array was also employed for comparison of one of the sources. Sound power levels were compared from the 50 Hz to the 10<th>000 Hz one-third octave bands using several methods. The results are compared to the sound power levels provided by the manufacturer.

CALIBRATION OF NOISE ANNOYANCE RATINGS AT WORK

Three methods for calibrating noise annoyance ratings were tested in a group of 206 persons from different work places. One was Master scaling, which involves calibration for differences in mean ratings as well as the slope of the psychophysical function for seven levels of a pink noise reference sound. The other two methods calibrated only for differences in mean ratings of reference sounds. The reference sounds were either the pink noises or verbal descriptions of three everyday sounds. Calibrations for differences in mean ratings leads to a sixfold increase of the variance explained by sound level. Calibrating for difference in slope did not lead to any further improvement. The described sounds worked only slightly worse than the recorded sounds as reference sounds.

Comparison of Earphone and Sound Field Methods for Estimating Noise Attenuation of Foam Earplugs

The Real Ear Attenuation at Threshold (REAT) of E-A-R (slow recovery) foam earplugs was determined, using three methods of presentation of the test tones during a single fitting of the earplug. The three presentation methods were (a) sound-field listening; (b) TDH49 earphone mounted in the shell of a circumaural earmuff; and (c) TDH49 earphone in a Model 51 cushion. Thresholds were tested once under each condition. Test frequencies were.125,.25,.5, 1.0, 2.0, 3.0, 4.0, 6.0, and 8.0 kHz. Comparison of the REAT values measured by the three methods indicated that the mean REAT obtained by the reference (Sound Field) method could be reliably estimated by both earphone methods for frequencies up to and including 4.0 kHz. However, the Sound Field REAT values of individual subjects could not be predicted reliably from their REAT determined by either type of earphone presentation. It is concluded that TDH49 earphones in standard audiometric earcushions could be used to check the overall effectiveness of slow recovery foam earplugs in the workplace. Further research is necessary to ascertain whether the audiometric earphone!earcushion test could be modified to achieve satisfactory reliability in assessing earplug fitting in individual workers.

Unknown sound evaluating method and apparatus

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Influence of a Reflecting Plane on the Reference Sound Source of Multi-blade Fan

Influence of a Reflecting Plane on the Reference Sound Source of Multi-blade Fan

Characteristics and Calibration of Reference Sound Sources

Characteristics and Calibration of Reference Sound Sources

Design and Analyis of Reverberant Room Experiments

Accurate measurements of sound power in a reverberant room using the substitution technique require that the means of the squared sound-pressure level (SPL) of the known source and unknown source be determined. Careful design of an experiment permits the errors due to the microphone traverse, the instrumention, and the source location to be separated. The technique of two-way analysis of variance with replication applied to a measurement of the SPL established by an air-conditioning condensing unit with only the fan operating reveals that (1) the observed variance in SPL is considerably greater than that observed for the Ilg Reference Sound Source and (2) strongly dependent on source location, with a small change of source location causing noticeable changes in the measured SPL. The variance due to source location for the 250-Hz 13-oct band suggests a pure tone exists in this band. Further experimentation shows that changes of a few degrees in the room temperature can also cause appreciable changes in the measured SPL for this band. Investigations of the details of the fan spectrum are continuing. Results of these experiments indicate that accurate measurements in a reverberant room require careful attention to details.

Statistical Behavior of Source-Receiver Locations in a Reverberant Room

The pure-tone, narrow-band, and 13-oct band probability distribution functions of the SPL for source positions (located on the floor) and receiver positions (located in the interior away from boundaries) were investigated for a random dipole source (Ilg Reference Sound Source), a dipole source (unbaffled loudspeaker), and a monopole source (loudspeaker) for frequencies from 100 to 4000 Hz. The experimental data indicate that an experiment in a reverberant room must be carefully defined. A theoretical model is advanced to explain the observed results.

Steady-State Noise Characteristics of Semireverberant Spaces

The use of a steady-state reference sound source, such as the Ilg Reference Sound Source, for determining the acoustic nature of semireverberant spaces is explored with emphasis on what precautions should be observed if useful eugineering results are to be obtained. For reasonable acoustic environments, the steady-state method can also be used to estimate the room absorption or, by the substitution technique, the sound power of an unknown source.

The Effect of Room Absorption on the Sound Power Output of the Ilg Reference Sound Source in a Reverberant Room

Previous work by others indicated differences in the sound power output of the Ilg depending upon the measurement techniques used. An experiment was performed in which the sound power output of the Ilg reference sound source (RSS) was determined from measurements of the space-time average of the pressure and the reverberation time as the room absorption was progressively increased by adding up to 14 panels (2ft×4ft×3 in.) of Owens Corning type 703 fiberglass. The results compared favorably with free-field measurements over a reflecting plane for low values of absorption and high frequencies but diverged for high values of absorption and low frequencies. Differences due to absorption were traced to using the Norris-Eyring equation for calculating absorption from the reverberation time. It is shown that use of a modified Sabine equation will yield the correct relationship between the absorption and reverberation time. Differences at low frequency disappear if the spatial pressure in the center of the room is corrected to the spatial pressure throughout the room as suggested by Waterhouse [J. Acoust. Soc. Amer. 27, 247 (1955)]. It is concluded that the sound power output of the RSS is independent of room absorption.